The present invention relates to positive-displacement machines. More particularly, this invention concerns a piston-displacement pump.
Positive-displacement machines are already well known and they usually include a hollow housing provided with an adjustable working element positioned in the housing between slidably mounted pistons of different cross-sections. The piston of relatively large cross-section is connected through a control device with a high-pressure chamber, to thereby regulate the position of the adjustable element.
Forces exercised on the adjustable element due to displacement of a workpiece create a fluctuating internal force applied on the adjustable element. This counteracting force must be taken up by the pistons.
Should the force operate in the direction towards the relatively large piston, then in order to achieve force-equilibrium, the pressure in the bore which receives the piston will rise. The rising of the pressure in this bore occurs due to compression of pressure fluid contained in the bore.
The adjustable element then moves towards this piston. Should the force change its direction towards the relatively small piston, then in order to achieve force-equilibrium, the pressure in the relatively large bore is reduced due to the expansion of the bore volume as the adjustable element moves towards the relatively small piston.
Such displacements make the adjustable elements oscillate between the pistons, which oscillation leads to noise due to air-body excitation in the housing.